My '69 280 SL auto trans behaves very well and exhibits none of this behaviour, cold or hot. It would be good to find out the cause of this issue, considering how many replied with the same problem.
I did notice that, after my engine was rebuilt, it doesn't shift down as well as it did before - probably the result of more or less vacuum from the 'new' engine. It's not so bad that I have tried to fix it, but the point is that these transmissions seem very sensitive to the inputs they receive, so it could be a matter of the (pressure) settings / adjustments?